Study on structural integrity of welded components using the LMM

Student thesis: Doctoral Thesis

Abstract

Industries, which have structures, subjected to high temperatures, such as the nuclear power plant industry, give paramount importance to structural integrity assessments due to the obvious catastrophic effect an unfortunate failure might cause. The presence of welds increases the susceptibility of premature failure within the structures. Hence identifying the structural response of welded components under cyclic loading conditions and developing methods to predict their safe life is of significant importance. The work within this thesis focuses on the investigation of cyclic plasticity and creep-cyclic plasticity interaction of welded components, and the consequential damage assessment using the Linear Matching Method (LMM). Firstly, a numerical investigation and parametric study on the cyclic plasticity behaviour of a butt-welded pipe under cyclic thermal and constant pressure load is undertaken. The most critical results are used to create limit load envelopes that may be used to design welded pipes within the specified range.Secondly, through a series of case studies, the effect of various complex loading conditions on the evolution and progress of fatigue damage, creep damage and creep-fatigue interaction of welded connectors, commonly found in power plants, are identified and discussed comprehensively using the Direct Steady Cycle Analysis (DSCA) and the extended Direct Steady Cycle Analysis(eDSCA) method within the Linear Matching Method Framework (LMMF). Finally, the subroutine is enhanced to account for any previous residual stress such as the welding residual stress (WRS) on the shakedown-ratchet limit interaction curves and the creep-fatigue endurance. With a welded flange case study, the effect of WRS on mean strain during the transient cycles and the fatigue damage at steady state is demonstrated.
Date of Award25 Nov 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsUniversity of Strathclyde
SupervisorHaofeng Chen (Supervisor) & David Nash (Supervisor)

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